More Americans suffer from chronic pain than heart disease, diabetes and cancer combined. Unfortunately, existing analgesics are not completely effective for all pain conditions and have serious side effects. These facts highlight what is undoubtedly a critical challenge for modern biomedical research-the need to provide pain relief without serious side effects. We will directly address this challenge by harnessing ectonucleotidases that are found endogenously in nociceptive (pain-sensing) circuits in dorsal root ganglia (DRG) and spinal cord. Ectonucleotidases degrade purine nucleotides (like ATP and ADP) that cause pain into adenosine-a compound that has analgesic properties in rodents and humans. Adenosine suppresses pain by acting through A1-adenosine receptors. To fully harness ectonucleotidases for the treatment of pain, we will identify all of the ectonucleotidases that metabolize nucleotides to adenosine in nociceptive circuits and then determine if these enzymes can be used alone or in combination to treat acute and chronic pain. We will utilize genetically modified mice that are missing these enzymes, recombinant ectonucleotidase proteins, behavioral assays and patch clamp electrophysiology for these experiments. In addition, we will use medicinal chemistry to synthesize adenosine prodrugs that can be converted into potent A1-adenosine receptor agonists by ectonucleotidases. We will measure the stability of these prodrugs in serum and use behavioral and physiological assays to assess analgesic efficacy and side effects. We will also test ectonucleotidases and prodrugs for efficacy in animal models of chronic inflammatory and neuropathic pain.